The process of monitoring and maintaining a gas production and distribution system is a difficult challenge. If done properly, this task includes processing massive quantities of data acquired over a large geographical area. Currently, gas transportation systems such as natural gas transportation systems (i.e. gas production, processing, pipeline and distribution systems) have very limited capability to acquire data, report data, organize data and monitor systems. One reason is the lack of harmonious data acquisition and communication systems. For example, acquiring gas transportation system data from multiple sensors at hundreds of locations, twenty-four hours a day, 365 days a year, merely creates large quantities of “unorganizable” data. Unorganizable data is not very useful because it cannot provide a sufficient overview of system operation, events, and phenomena.
A typical gas distribution system is partitioned into districts. Large pipes (gas mains) supply gas to districts through manifolds at district locations. A manifold is essentially a pipe with several openings for making several connections. In an average metropolis, hundreds of district sites exist and hundreds of thousands of supply lines are unmonitored. Most gas companies still utilize manual data collection systems. They send field technicians out to district sites to manually measure and record system parameters at various locations. Measurements are often hand written in a logbook. Thus, data received from various points in a gas system cannot be correlated by location or synchronized in time to provide a comprehensive overview of system operation. While significant sensor technology is available to periodically monitor or detect gas system parameters at district locations, data collection and data management tools for evaluating an entire gas transportation system are clearly deficient.
Valuable data can be gathered at ports in the transportation system (typically at district sites). However, currently there is not an efficient way to provide useful data to a central system. Even if data was available at a central location there is no efficient way to organize or manipulate the data to make it useful. As a result, characterization of an operational gas system is nearly impossible. Due to the lack of useable data, system wide events within a gas transportation system are not well understood. Further, system wide coordination of gas pressure control is not achievable. A gas company could maximize system performance, detect leaks, anticipate explosions or spills, and save millions of dollars annually if they could adequately monitor system wide events. Currently, data acquisition and process control systems for gas transportation systems lack comprehensive real time, dynamic management capabilities because of the less than perfect communication, control, and data processing systems.
FIG. 1, illustrates a hydrocarbon fuel production, pipeline, and distribution system or gas transportation system 3. Gas producers capture gas from the earth 1 and deliver the gas to distributors. Gas is extracted from a well 28, proceeds through a valve 5, is processed by a plant 11, and is compressed or pressurized by a pump 10 for delivery through a pipeline 4. The pipeline 4 transports gas to locations where it will be consumed, such as a first city 7, a second city 33 or a power plant 9. A second well 30 may also supply gas to the pipeline 4 via a plant 111 and a second pump 110.
In a gas transportation system, ownership of the gas may change many times. When ownership changes, meters 6 are utilized to measure the quantity of gas supplied, sold or purchased. A typical transfer of ownership would involve transfer from a producer to a distributor, or from distributor to a consumer. Additionally, mechanical pressure regulators 2 are typically present at custody transfer points to maintain a predetermined line pressure proximate to the meters 6. Pressure control is important to ensure meter accuracy. Additional pump substations 24 may be required to overcome frictional losses and boost sagging pressures within the gas system 3.
Often, a gas producer can utilize a distribution system (such as that associated with second city 33) as part of a gas transportation system. Thus, a producer's gas may travel through a city distribution system (second city 33) and supply a consumer (such as power plant 9) beyond the distribution system. Distribution system owners generally charge producers a transportation fee to transport gas through their distribution system(s).
All United States gas producers and distributors are regulated by either a state-sanctioned Department of Transportation (DOT) or the United States DOT. Maximum allowable line pressure and other regulations are strictly enforced by these DOT's. Thus, a distributor wants to maximize the pass-through volume by maintaining higher pressures, but must comply with DOT maximum pressure requirements and other regulations. Higher line pressures also create increased leakage in the system. However, without having adequate system wide data acquisition and pressure control, it is difficult to maximize profits and to comply with the regulations. Gas companies may acquire and store sensor data, but without adequate infrastructure to coordinate the data, the sensor data is virtually useless.
When a problem occurs in a gas transportation system, maintenance workers typically visit various locations and take a series of measurements. Based on these measurements, the maintenance worker may be able to locate faulty equipment or other problems. Often times however, due to the lack of data coordination, these measurements neither reveal the cause of the problem nor the solution to the problem.
Mechanical pressure regulators 2 have short lifetimes due to their moving parts and the harsh environment in which they must operate. A defective mechanical regulator located miles away from a detected problem may be the source of the problem. Manually troubleshooting a gas transportation system is typically accomplished by a procedure based on learned assumptions. This method is unstructured, time consuming and costly. Further, the test measurements are often manually recorded with a pen and paper and are discarded after a problem is solved. Thus, recorded or historical data is often unavailable or unorganized and therefore is useless.
Problems caused by impurities such as slugs of water or sludge entering the system can cause moving obstructions. Currently, detecting and curing moving obstructions is like “chasing a ghost.” Impurities can cause inefficiencies such as loss of system capacity or premature failure of devices. Impurities can plug filters, meters, regulators or even consumer appliances. Currently there is no way of monitoring events such as the existence and movement of impurities.
FIG. 2 illustrates a more detailed view of a typical distribution system, such as that of the second city 33. Mechanical regulators are located at district sites 27 (denoted by black dots not all numbered) for controlling gas pressure to a district. A gas distribution system provides redundant paths or “feeds” to most locations. Thus, pressure or flow measurements on feed lines do not provide sufficient data to understand gas flow characteristics in a distribution system (i.e. which feed lines, main lines and/or district regulators supply how much gas to various districts). The gas company must still consider managing a massive volume of “loose” data. Typically, gas distribution companies cannot coordinate the data and identify where, why, and how loss occurs. It is also common for a gas company to manually adjust pressure settings at the district locations depending on seasonal demand and other dynamic phenomena.
A typical district site does not have access to power or communication lines. As a result, electronic communication and control at district locations has been very limited or non-existent. Further, implementing such infrastructure has been generally regarded as dangerous and prohibited by high implementation costs. What is needed is an efficient method for acquiring and communicating data and an efficient method for managing a gas transportation system data such that profits can be increased and disasters can be avoided.